"just starting" vs "starting"

Question

I can't get the difference between these ones in the following context. In PEU, Swan is talking about the differences between uses of the present progressive and the going to structure in sentences about the future. What he says is

We often use the present progressive with verbs of movement, to talk about actions which are just starting.

and

Another use of the going to structure is to predict the future on the basis of present evidence - to say that a future action or event is on the way, or starting to happen

He also provides the following examples:

Look at the sky. It's gonna rain.

and

Are you coming to the pub?

Could you explain the difference between the phrase using examples?

Answer 1

If you're asking for the difference between starting and just starting, that is, what does the word "just" add to the meaning, there's a fine shade of difference.

If it's just starting to rain, you've felt the first few raindrops of a rain shower that will grow gradually in its intensity. If it's a "cloudburst", a sudden downpour which comes all at once, we wouldn't say "it's just starting to rain".

If the movie is "just starting", it's at the opening scene.

Have you played guitar long?
-- No, I'm just starting. I know a few basic chords.

So "just" refers to the earliest moments of the beginning. "The beginning of the beginning."

P.S. If you want to know what he means by predicting the (imminent) future on the basis of present evidence:

The vase is going to fall over! (maybe someone knocked into the table and the vase has started to wobble)

Don't inflate the tire any higher! It's going to burst! (maybe you can see a bubble forming)

But there is no marked difference between the imminent future, the close future, or the distant future.

The almanac predicts that this summer is going to be a hot one.

My aunt is going to take a trip to China some day.